U.S. patent application number 10/532240 was filed with the patent office on 2006-07-13 for display device adjusting method and display device.
Invention is credited to Yutaka Ozaki.
Application Number | 20060152468 10/532240 |
Document ID | / |
Family ID | 33156673 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060152468 |
Kind Code |
A1 |
Ozaki; Yutaka |
July 13, 2006 |
Display device adjusting method and display device
Abstract
An LED of each of colors, red, green and blue, undergoes PWM
control independently in a unit emission period to emit light,
luminance/chromaticity meter 31 measures the chromaticity of the
light, a difference is calculated between the measured value and
target white balance value, a duty ratio is corrected on the LED of
each color corresponding to the difference to light the LED of each
color again, and the duty ratio for the LED of each color such that
the difference falls within a predetermined allowable range is
stored in duty ratio storage register 21, 22 or 23.
Inventors: |
Ozaki; Yutaka; (Ibaraki,
JP) |
Correspondence
Address: |
NATH & ASSOCIATES
112 South West Street
Alexandria
VA
22314
US
|
Family ID: |
33156673 |
Appl. No.: |
10/532240 |
Filed: |
March 26, 2004 |
PCT Filed: |
March 26, 2004 |
PCT NO: |
PCT/JP04/04291 |
371 Date: |
August 31, 2005 |
Current U.S.
Class: |
345/102 |
Current CPC
Class: |
G09G 2320/029 20130101;
G09G 3/2014 20130101; G09G 2360/145 20130101; G09G 2320/0626
20130101; G09G 2320/0666 20130101; G09G 2320/0693 20130101; G09G
3/32 20130101; G09G 2310/0235 20130101; G09G 2330/021 20130101;
G09G 3/006 20130101; G09G 3/3413 20130101; G09G 2320/064 20130101;
G09G 2320/0233 20130101 |
Class at
Publication: |
345/102 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2003 |
JP |
JP 2003-098488 |
Claims
1. An adjustment method of a display device, comprising: an LED
emission step of performing PWM control independently on an LED of
each of colors, red, green and blue, in a unit emission period to
cause the LED to emit light; a measuring step of measuring
chromaticity of the light; a calculating step of calculating a
difference between a measured value obtained in the measuring step
and a target white balance value; a correcting step of correcting a
duty ratio of a PWM signal on the LED of each of colors in the LED
emission step corresponding to the difference obtained in the
calculating step; and a duty ratio storing step of storing a duty
ratio for the LED of each of colors in a storage when the
difference calculated in the calculating step falls within a
predetermined allowable range.
2. The adjustment method of a display device according to claim 1,
wherein an adjustment of the display device is made in such a state
that an LCD panel is attached to a front face of the LED and that
the LCD panel is driven.
3. The adjustment method of a display device according to claim 1,
wherein in the correcting step, the duty ratio of the PWM signal
for the LED of each of colors is corrected in consideration of a
distribution range of the chromaticity of the LED of each of
colors.
4. The adjustment method of a display device according to claim 1,
wherein the duty ratio is corrected independently on LEDs of the
same color corresponding to the difference obtained in the
calculating step, and independent duty ratios for the LEDs of the
same color are stored in the duty ratio storing step.
5. A display device comprising: a duty ratio storage which is
comprised of writable memory and stores therein a duty ratio to
perform PWM control independently on an LED of each of colors, red,
green and blue, in a unit emission period, independently for each
LED; a PWM controller which forms a PWM signal based on the duty
ratio stored in the duty ratio storage independently for each LED
to perform PWM control independently on the LED of each of colors
in the unit emission period; and a signal line connected to the
duty ratio storage to input the duty ratio to the duty ratio
storage.
6. The display device according to claim 5, wherein the duty ratio
storage stores the duty ratio provided with a white balance
adjustment via the signal line.
7. The display device according to claim 5, wherein the duty ratio
storage stores independent duty ratios for LEDs of the same color,
and the PWM controller forms independent PWM signals for the LEDs
of the same color to perform PWM control independently on the LEDs
of the same color in a unit emission control.
Description
TECHNICAL FIELD
[0001] The present invention relates to an adjustment method of a
display device particularly having LEDs (Light-Emitting Diode) of
three primary colors, R, G, B, and the display device.
BACKGROUND ART
[0002] Conventionally, as a liquid crystal display device using
LEDs of three primary colors, R (red)-G (green)-B (blue), liquid
crystal display devices of field sequential system (hereinafter,
referred to as an FS system) have been implemented, for example, as
disclosed in JP 2000-241811. In the FS-system liquid crystal
display device, three-color LEDs are provided on the back surface
of a liquid crystal shutter, each of the LEDs is sequentially
lighted at high speed while opening and closing the liquid crystal
shutter at each pixel position to be synchronized with lighting of
the LEDs, and thereby, a desired color can be displayed at each
pixel position.
[0003] For example, in the case of displaying red, the liquid
crystal shutter is opened during a period of time a red LED emits
light, and then closed during a period of time a green LED emits
light and a period of time a blue LED emits light. The case of
displaying green or blue is the same, and the liquid crystal
shutter is opened only during a period of time the LED of desired
color emits light, and closed during periods of time the other LEDs
emit light.
[0004] Further, opening the liquid crystal shutter for periods
during which red and green LEDs emit light enables Y (Yellow) to be
displayed, opening the liquid crystal shutter for periods during
which red and blue LEDs emit light enables M (Magenta) to be
displayed, opening the liquid crystal shutter for periods during
which green and blue LEDs emit light enables C (Cyan) to be
displayed, and opening the liquid crystal shutter for all the
periods during which red, green and blue LEDs emit light enables W
(White) to be displayed.
[0005] In such an FS system, by lighting three-color LEDs
sequentially at speed higher than human visual reaction speed,
color display is implemented by additive color process. Then,
adopting the FS system eliminates the need of color filter, and
enables sharpened color display to be performed.
[0006] However, it is inevitable that an LED of each of colors, R,
G, B, has a few fluctuations in emission wavelength with products
due to fluctuations in products when manufactured, and as a result,
complicated operation is required to achieve the desired white
balance. For example, a method is used of making a fine adjustment
to resistance or the like of an LED of each color assembled into a
display device, or of selecting an LED of each color such that the
desired white balance is achieved, but there arises a problem that
the operation requires some effort.
DISCLOSURE OF INVENTION
[0007] It is a principal object of the present invention to provide
an adjustment method of a display device and display device
enabling a white balance adjustment to be made with ease even when
there are fluctuations in emission characteristics of LEDs. It is a
further object of the present invention to reduce current
consumption when such a white balance adjustment is made.
[0008] The object is achieved by controlling emission of an LED of
each color during a unit emission period using a PWM signal, and
storing in storage a duty ratio of the PWM signal for the LED of
each color such that the white balance falls within an allowable
range. Further, rough luminance adjustment is first made by storing
a minimum voltage value for each color when a luminance higher than
a target is obtained in a state where the duty ratio is maximum,
and fine luminance adjustment is then made by varying the duty
ratio of the PWM signal while applying the stored applied voltage
of fixed value, where by current consumption can be reduced, in
addition to the fact that the white balance is adjusted with
excellence.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a block diagram illustrating a configuration of an
LED driving device of an embodiment;
[0010] FIG. 2 is a diagram showing minimum voltage values required
to obtain a desired luminance in an LED of each color;
[0011] FIG. 3 is a block diagram illustrating a configuration of a
driving voltage setting device according to the embodiment;
[0012] FIG. 4 is a flowchart to explain processing for setting an
applied voltage and a duty ratio in the driving voltage setting
device;
[0013] FIG. 5 is a flowchart to explain processing for setting a
duty ratio to obtain the desired white balance;
[0014] FIG. 6 is a chromaticity spatial diagram to explain the
processing for setting a duty ratio to obtain the desired white
balance; and
[0015] FIG. 7 is a waveform diagram to explain the operation of the
LED driving device.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016] An embodiment of the present invention will specifically be
described below with reference to accompanying drawings.
[0017] In FIG. 1, "10" denotes an LED driving device as a whole.
LED driving device 10 is provided in a liquid crystal display
device, and drives LEDs of three colors, R, G and B, provided on
the back face of a liquid crystal panel. Further, this embodiment
describes the case of applying the present invention to a liquid
crystal display device of field sequential system, as an
example.
[0018] LED driving device 10 has R (red) applied voltage storage
register 11, G (green) applied voltage storage register 12 and B
(blue) applied voltage storage register 13. Each of the registers
11, 12 and 13 stores voltage values to apply to the R, G, or B LED,
respectively. Each of the registers 11, 12 and 13 is connected to
storage value setting bus 14, and applied voltage values for the
LED of each color are stored in each of the registers 11, 12 and 13
via storage value setting bus 14 when a product of LED driving
device 10 is shipped.
[0019] The applied voltage value for the LED of each color output
from each of the registers 11, 12 and 13 is input to register
selecting circuit 15. Register selecting circuit 15 further
receives as its inputs a red-LED emission timing signal TR,
green-LED emission timing signal TG, and blue-LED emission timing
signal TB, and based on the emission timing signal, selects either
the applied voltage value for R, G or B to output.
[0020] For example, when the red-LED emission timing signal TR has
a logic value of "1", and each of the green-LED emission timing
signal TG and blue-LED emission timing signal TB has a logic value
of "0", the circuit 15 selects the applied voltage value stored in
R applied voltage storage register 11. In the case of this
embodiment, since display is performed in the field sequential
system, for example, when the field frequency is assumed to be 65
Hz, the LED of each color is lighted sequentially with the
three-time frequency, 195 Hz. In other words, register selecting
circuit 15 selects and outputs voltage values stored in R applied
voltage storage register 11, G applied voltage storage register 12
and B applied voltage storage register 13 in turn at intervals of
about 5 mS.
[0021] The applied voltage value selected by register selecting
circuit 15 is converted into an analog value by digital analog (DA)
converting circuit 17 in applied voltage forming circuit 16, and
then output to voltage varying circuit 18. Voltage varying section
18 converts a voltage generated in power supply voltage generating
circuit 19 into a voltage corresponding to an analog value input
from digital analog converting circuit 17, and supplies the voltage
to LED unit 20.
[0022] Thus, LED driving device 10 has the registers 11, 12 and 13
that store voltage values to apply to LEDs of respective colors,
and converts a voltage generated in power supply voltage generating
circuit 19 into a value stored in the register 11, 12 or 13 to
supply to a corresponding one of the LEDs. By this means, it is
possible to reduce power consumption as compared with the case of
applying the same voltage to the LED of each color.
[0023] FIG. 2 shows minimum applied voltage values (hereinafter
referred to as minimum emission voltages) required to obtain a
desired luminance in an LED of each color. As can be seen from the
figure, minimum emission voltages of the green LED and blue LED are
almost the same, while minimum emission voltages of the red LED are
lower than those minimum emission voltages.
[0024] Applied voltage storage registers 11, 12 and 13 of LED
driving device 10 store minimum emission voltage values of the LEDs
of respective colors. Among the stored minimum emission voltage
values, values of the red LED are actually lower than values of the
green LED and blue LED. In other words, it is possible to apply a
minimum voltage required for each of the LEDs, and it is thus
possible to reduce current consumption.
[0025] Further, as can be seen from FIG. 2, even in the LED of each
color, fluctuations arise in minimum emission voltage. For example,
the minimum emission voltage fluctuates in a range of 1.75V to
2.45V in the red LED, while fluctuating in a range of 2.9V to 3.9V
in the green LED and blue LED. The fluctuations in minimum emission
voltage are due to fluctuations in individual product caused by LED
manufacturing.
[0026] In this embodiment, not only setting applied voltages for
the red LED lower than applied voltages for the green and blue
LEDs, applied voltages in consideration of fluctuations in minimum
emission voltage among individual products are stored in the
registers 11, 12 and 13 for respective colors. It is thereby
possible to obtain a desired luminance of the LED of each color
while reducing power consumption. Applied voltage values are stored
in the registers 11, 12 and 13 for respective colors via storage
value setting bus 14, as described later.
[0027] Referring to FIG. 1 again, a configuration of LED driving
device 10 will be described below. LED driving device 10 has R duty
ratio storage register 21, G duty ratio storage register 22 and B
duty ratio storage register 23. Each of the registers 21, 22 and 23
stores duty ratio data of PWM signal to perform PWM control on the
LED of each color, R, G, or B, respectively. Each of the registers
21, 22 and 23 is connected to storage value setting bus 14, and the
duty ratio data for the LED of each color is stored in each of the
registers 21, 22 and 23 via storage value setting bus 14 when the
product of LED driving device 10 is shipped.
[0028] The duty ratio data for the LED of each color output from
each of the registers 21, 22 and 23 is output to PWM waveform
forming circuit 24, 25 or 26, respectively. Each of PWM waveform
forming circuits 24, 25 and 26 forms a PWM waveform corresponding
to the duty ratio data in synchronization with a clock signal
CLK.
[0029] PWM waveform forming circuit 24, 25 or 26 outputs a PWM
waveform to the base of transistor 27, 28 or 29 based on the
red-LED emission timing signal TR, green-LED emission timing signal
TG, or blue-LED emission timing signal TB, respectively. In each of
transistors 27, 28 and 29, the collector is connected to an output
terminal of the LED of R, G or B, while the emitter is grounded,
respectively.
[0030] By this means, during an emission period of the red LED,
only the red-LED emission timing signal TR has a logic value of
"1", a PWM signal is only output from PWM waveform forming circuit
24 provided for the red LED, the current corresponding to the PWM
signal flows into the red LED, and the red LED emits light.
Similarly, during an emission period of the green LED, only the
green-LED emission timing signal TG has a logic value of "1", a PWM
signal is only output from PWM waveform forming circuit 25 provided
for the green LED, the current corresponding to the PWM signal
flows into the green LED, and the green LED emits light. During an
emission period of the blue LED, only the blue-LED emission timing
signal TB has a logic value of "1", a PWM signal is only output
from PWM waveform forming circuit 26 provided for the blue LED, the
current corresponding to the PWM signal flows into the blue LED,
and the blue LED emits light.
[0031] FIG. 3 illustrates a configuration of driving voltage
setting device 30 for setting voltage values to store in applied
voltage storage registers 11, 12 and 13 for respective colors. In
addition, driving voltage setting device 30 has the configuration
capable of obtaining duty ratio data for the LED of each color to
store in duty ratio storage register 21, 22 or 23, as well as
voltage values for the LED of each color to store in applied
voltage storage register 11, 12 or 13.
[0032] Driving voltage setting device 30 has luminance/chromaticity
meter 31 to measure the luminance and chromaticity of transmission
light from the LCD panel. In addition, the light emitted from LED
unit 20 is incident on luminance/chromaticity meter 31 via a light
guide plate (not shown) and LCD panel 40. The predetermined voltage
is applied to the liquid crystal at each pixel position from an LCD
driving circuit (not shown) at predetermined timing to drive the
liquid crystal in open or close, whereby LCD panel 40 passes or
shields the light emitted from the LED. In addition, it is assumed
that LED unit 20, the light guide plate and LCD panel 40 are
assembled in the same way as in shipment of the product.
[0033] The data of luminance and chromaticity obtained from
luminance/chromaticity meter 31 is output to microcomputer 32.
Driving voltage setting device 30 has applied voltage setting
section 33 and duty ratio setting section 34, and a voltage value
set in applied voltage setting section 33 is output to DA
converting circuit 17 of LED driving device 10, while the duty
ratio data set in duty ratio setting section 34 is output to PWM
waveform forming circuits 24, 25 and 26. The set voltage value and
set duty ratio are designated from microcomputer 32. In other
words, the microcomputer recognizes the set voltage value and duty
ratio.
[0034] Microcomputer 32 judges whether the luminance and
chromaticity meet respective desired values beforehand set, and
when the desired values are met, writes the voltage value applied
at this point in applied voltage storage register 11, 12 or 13, and
further writes the duty ratio in duty ratio storage register 21, 22
or 23, via storage value setting bus 14. In other words,
microcomputer 32 has the function as means for writing storage data
in applied voltage storage registers 11, 12 and 13 and in duty
ratio storage registers 21, 22 and 23.
[0035] Referring to FIG. 4, processing will specifically be
described below for driving voltage setting device 30 to record
applied voltage values (minimum emission voltages) in applied
voltage storage registers 11, 12 and 13 for respective colors and
further record the duty ratio data in duty ratio storage registers
21, 22 and
[0036] Driving voltage setting device 30 starts the processing in
step ST10, and in the subsequent step, ST11, sets duty ratios in
duty ratio setting section 34. Since the case of FIG. 4 shows
processing for setting a voltage to apply to the red LED, the
setting device 30 sets the ON duty ratio of the red LED at a
maximum value, while setting ON duty ratios of the green and blue
LEDs at zero. In other words, PWM waveform forming circuit 24 is
given data with the ON duty ratio of the maximum value, while PWM
waveform forming circuits 25 and 26 are given data with the ON duty
ratio of "0". Instep ST12, microcomputer 32 sets a target
luminance.
[0037] In step ST13, applied voltage setting section 33 sets a
minimum applied voltage value Vmin (for example, 1.5V), and voltage
varying circuit 18 converts the voltage generated in power supply
voltage generating circuit 19 into the set voltage to apply to LED
unit 20. At this point, since only the red PWM waveform forming
circuit 24 outputs a PWM signal with the maximum ON duty ratio, the
red LED is only in a state for enabling light emission.
[0038] In step ST14, microcomputer 32 judges whether or not the
measured luminance obtained by luminance/chromaticity meter 31 is
greater than the target luminance. When the measured luminance is
less than the target luminance, microcomputer 32 shifts to the
processing of step S15, increases a set applied voltage in applied
voltage setting section 33 by k (for example, 0.1V), and makes the
judgment in step ST14 again.
[0039] A positive result obtained in step ST14 means that the
minimum voltage required to obtain a desired luminance is currently
being applied to the red LED, and the processing flow shifts to
step ST16 where microcomputer 32 writes the voltage value currently
set in applied voltage setting section 33 in R applied voltage
storage register 11. Thus, the minimum emission voltage value
required for the red LED to obtain a desired luminance is stored in
R applied voltage storage register 11.
[0040] In the subsequent step, ST17, microcomputer 32 judges
whether or not the measured luminance agrees with the target
luminance. When agreement is not obtained, microcomputer 32 shifts
to step ST18, decreases the ON duty ratio set in duty ratio setting
section 32 by r, and returns to step ST17.
[0041] A positive result obtained in step ST17 means that it is
possible to cause the red LED to emit light with the desired
luminance using the PWM signal with the duty ratio currently set in
duty ratio setting section 34, and the processing flow shifts to
step ST19 where microcomputer 32 writes the duty ratio currently
set in duty ratio setting section 34 in R duty ratio storage
register 21. Thus, the duty ratio for the red LED to obtain the
desired luminance is stored in R duty ratio storage register
21.
[0042] In other words, the processing of steps ST17 to ST19
indicates that the duty ratio is set to perform fine luminance
control using the PWM signal so as to bring the luminance close to
the target luminance after setting in steps ST14 to ST16 the
minimum applied voltage enabling the target luminance to be
obtained. In the subsequent step, ST20, driving voltage setting
device 30 finishes the processing for writing data in R applied
voltage storage register 11 and R duty ratio storage register
21.
[0043] In addition, herein described is the processing for writing
data in R applied voltage storage register 11 and R duty ratio
storage register 21, and similar procedures are carried out to
perform processing for writing data in G and B applied voltage
storage registers 12 and 13 and G and B duty ratio storage
registers 22 and 23.
[0044] Referring to FIG. 5, procedures will be described below to
store in the registers 21, 22 and 23 duty ratios for respective
colors to obtain the desired white balance.
[0045] Driving voltage setting device 30 starts white balance
adjustment processing in step ST30, and in the subsequent step,
ST31, lights the LEDs of respective colors sequentially using
applied voltages stored in applied voltage storage registers 11, 12
and 13 and PWM signals with duty ratios stored in duty ratio
storage registers 21, 22 and 23, while driving LCD panel 40 using
the LCD driving circuit (not shown).
[0046] Actually, LED driving device 10 applies voltages for the
LEDs of respective colors stored in applied voltage storage
registers 11, 12 and 13 sequentially to LED unit 20, and in
synchronization with the voltage application, PWM waveform forming
circuits 24, 25 and 26 form PWM signals for the LEDs of respective
colors corresponding to the duty ratios stored in duty ratio
storage registers 21, 22 and 23.
[0047] In other words, in step ST31 is performed actual LED driving
and LCD driving in the field sequential system. It is herein
assumed that data stored in applied voltage storage registers 11,
12 and 13 and duty ratio storage registers 21, 22 and 23 is data
set as shown in FIG. 4.
[0048] In step S32, luminance/chromaticity meter 31 measures the
chromaticity of a display color. FIG. 6 shows measured degrees of
chromaticity plotted in the chromaticity space. Then, microcomputer
32 calculates a difference between the measured chromaticity and a
target value of the white balance, and duty ratio setting section
34 corrects duty ratios to set corresponding to the difference to
supply to PWM waveform forming circuits 24, 25 and 26.
Microcomputer 32 is capable of reading out duty ratios for
respective colors stored in duty ratio storage registers 21, 22 and
23, and based on the read duty ratios for respective colors and the
difference between the measured chromaticity and target value of
the white balance, designates the duty ratios for respective colors
to next set in duty ratio setting section 34. By this means, the
duty ratios for respective colors are set at values such that the
target white balance is obtained.
[0049] Specifically, it is first judged in step ST33 whether or not
the Y coordinate of the measured chromaticity is within a white
allowable range as shown in FIG. 6, and it is further judged in
step ST34 whether or not the X coordinate of the measured
chromaticity is within the white allowable range as shown in FIG.
6. When a negative result is obtained in either step ST33 or step
ST34, the processing flow shifts to step ST3S, and duty ratio
setting section 34 corrects the duty ratio.
[0050] The correction of the duty ratio is made based on the
difference in direction and scale between a target point of the
white balance and the measured chromaticity. In the case of this
embodiment, microcomputer 32 considers a distribution range of
chromaticity of the LED of each color, and corrects the duty ratio
of the PWM signal for the LED of each color. For example, the
amount of the difference is allocated in proportion to the amount
of correction of the duty ratio for the LED of each color in
consideration of the distribution range of chromaticity of the LED
of each color, whereby it is possible to find the duty ratio such
that the white balance falls within the allowable range promptly in
a small number of corrections.
[0051] For example, as shown in FIG. 6, a case is considered where
the Y coordinate of a measured value is larger than that of the
target point, and that the X coordinate of the measured value is
smaller than that of the target point. Respective distribution
ranges of the LEDs of colors, R, G and B, in chromaticity space are
generally as shown in FIG. 6. Therefore, in order to decrease the Y
component and increase the X component to bring the white balance
close to the target point, for example, the red ON duty ratio is
increased, while the green ON duty ratio is decreased.
[0052] By thus setting ON duty ratios in proportional allocation as
described below, it is possible to find respective duty ratios for
the colors such that the target white balance is obtained a small
number of settings.
[0053] Obtaining positive results in both steps ST33 and ST34 mean
that the white balance is in the white allowable range, and
therefore, driving voltage setting device 30 shifts to step ST36,
stores duty ratios for red, green and blue currently set in duty
ratio setting section 34 respectively in duty ratio storage
registers 21, 22 and 23, and finishes the white balance adjustment
processing in the subsequent step, ST37.
[0054] Thus, driving voltage setting device 30 starts with the duty
ratio such that a desired luminance is obtained on the LED of each
of colors, R, G and B, independently, measures the white balance of
the actual display color, corrects respective duty ratios for the
colors corresponding to the measured values, while searching for
duty ratios such that the desired white balance is obtained, and
stores respective duty ratios for the colors at the time the
desired white balance is obtained in corresponding duty ratio
storage registers 21, 22 and 23.
[0055] In this way, driving voltage setting device 30 corrects the
duty ratio for each color, thereby makes an adjustment to the white
balance, and therefore, is capable of adjusting the white balance
finely with ease. Further, by storing duty ratios to adjust the
white balance in writable registers 21, 22 and 23, it is possible
to write duty ratios specific to each product while actually
measuring the chromaticity of the product. Therefore, even when
there are fluctuations in LED, light guide plate and LCD panel for
each product, it is possible to obtain the desired white balance in
each product.
[0056] The operation of LED driving device 10 of this embodiment
will be described below with reference to FIG. 7. In LED driving
device 10, in an red-LED emission period LR, register selecting
circuit 15 first selects an output of R applied voltage storage
register 11 among from outputs of applied voltage storage registers
11, 12 and 13, and voltage varying circuit 18 forms a voltage of
2.2V corresponding to the output of R applied voltage storage
register 11, and supplies the voltage of 2.2V to LED unit 20 as
shown in FIG. 7(a).
[0057] When the red-LED emission timing signal TR rises at time t2
during the red-LED emission period LR, PWM waveform forming circuit
24 outputs a PWM signal with the duty ratio stored in R duty ratio
storage register 21 to transistor 27, and thereby the red LED emits
light in the luminance corresponding to the PWM signal. Then, when
the red-LED emission timing signal TR falls at time t3, the output
from PWM waveform forming circuit 24 is halted, and register
selecting circuit 15 selects an output of G applied voltage storage
register 12, substituting for the output of R applied voltage
storage register 11.
[0058] By this means, in a green-LED emission period LG, LED
driving device 10 forms a voltage of 3.3V in voltage varying
circuit 18 corresponding to data of G applied voltage storage
register 12, and supplies the voltage of 3.3V to LED unit 20. When
the green-LED emission timing signal TG rises at time t4 during the
green-LED emission period LG, PWM waveform forming circuit 25
outputs a PWM signal with the duty ratio stored in G duty ratio
storage register 22 to transistor 28, and thereby the green LED
emits light in the luminance corresponding to the PWM signal. Then,
when the green-LED emission timing signal TG falls at time t5, the
output from PWM waveform forming circuit 25 is halted, and register
selecting circuit 15 selects an output of B applied voltage storage
register 13, substituting for the output of G applied voltage
storage register 12.
[0059] By this means, in a blue-LED emission period LB, LED driving
device 10 forms a voltage of 3.4V in voltage varying circuit 18
corresponding to data of B applied voltage storage register 13, and
supplies the voltage of 3.4V to LED unit 20. When the blue-LED
emission timing signal TB rises at time t6 during the blue-LED
emission period LB, PWM waveform forming circuit 26 outputs a PWM
signal with the duty ratio stored in B duty ratio storage register
23 to transistor 29, and thereby the blue LED emits light in the
luminance corresponding to the PWM signal. Then, when the blue-LED
emission timing signal TB falls at time t7, the output from PWM
waveform forming circuit 26 is halted, and register selecting
circuit 15 selects an output of R applied voltage storage register
11, substituting for the output of B applied voltage storage
register 13.
[0060] Thereafter, in the same way as the foregoing, repeated are
the red-LED emission period LR, green-LED emission period LG and
blue-LED emission period LB, whereby color display is carried out
in the field sequential system.
[0061] In addition, in the case of this embodiment, each of the LED
emission periods LR, LG and LB is set at about 5 mS, and the PWM
signal output period for each color is set at about 2000 .mu.s.
Further, a waveform of the PWM signal has a unit cycle of 50 .mu.s,
and the duty ratio in the unit cycle is stored in each of the duty
ratio storage registers 21 to 23. In the case of this embodiment,
duty ratios of eight bits (=256 different ratios) are stored in
each of the duty ratio storage registers 21 to 23.
[0062] Thus, according to this embodiment, the LED of each of
colors, red, green and blue, undergoes PWM control independently
during a unit emission period to emit light, luminance/chromaticity
meter 31 measures the chromaticity of the light emission, a
difference is calculated between the measured value and target
white balance value, the duty ratio for the LED of each of the
colors is corrected corresponding to the difference to light the
LED of each of the colors again, and the duty ratio for the LED of
each of the colors such that the difference falls within a
predetermined allowable range is stored in the duty ratio storage
register 21, 22 or 23. It is thus possible to implement an
adjustment method of a display device and the display device
capable of making a white balance adjustment readily and finely
even when there are fluctuations in emission characteristics of LED
and LCD panel 40.
[0063] Further, rough luminance adjustment is first made by storing
a minimum voltage value for each color when a luminance higher than
a target is obtained in a state where the duty ratio is maximum,
and fine luminance adjustment is then made by varying the duty
ratio of the PWM signal while applying the stored applied voltage
of fixed value, whereby current consumption can be reduced, in
addition to the fact that white balance is adjusted with
excellence.
[0064] In addition, in the aforementioned embodiment, for
simplicity in drawings and descriptions, LED unit 20 is comprised
of two red LEDs, two blue LEDs and one green LED, but the present
invention is not limited to such the number of the LED of each
color. Further, any number is available as the number of LED units
20, and it may be possible to set the driving voltage and duty
ratio of an LED of each color independently for each of the LED
units to store in memory.
[0065] Moreover, it maybe possible that a variable voltage is
applied independently to each of LEDs of the same color, the
luminance is detected independently on each of LEDs of the same
color, a minimum applied voltage value when a luminance higher than
a desired value is detected is set as a driving voltage value on
each of LEDs of the same color and stored in applied voltage
storage register 11, 12 or 13, and that each of LEDs is driven with
the voltage value. In this way, even when there are fluctuations in
driving voltage required to obtain the desired luminance between
LEDs of the same color, it is possible to drive each of the LEDs of
the same color with the minimum driving voltage corresponding to
the fluctuations, and thus, current consumption can further be
reduced.
[0066] Similarly, it may be possible that each of LEDs of the same
color is controlled using the PWM signal with a different duty
ratio, the duty ratio for each of the LEDs of the same color when a
desired luminance and white balance is detected is stored
independently in duty ratio storage register 21, 22 or 23, and that
each of the LEDs undergoes PWM control using the duty ratio. In
this way, even when there are fluctuations in duty ratio required
to obtain the desired luminance and white balance between LEDs of
the same color, each of the LEDs can be controlled in PWM using the
duty ratio corresponding to the fluctuations, and it is thereby
possible to make a finer luminance adjustment and white balance
adjustment.
[0067] Further, the above-mentioned embodiment describes the case
of using a liquid crystal display device in the field sequential
system, but the present invention is not limited to such a case and
widely applied to display device stoper form color display using
LEDs of three colors, R, G and B. Furthermore, the above-mentioned
embodiment describes the case of applying the independent voltage
for each color to an LED of each color, but the present invention
is not limited to such a case and enables the same effects to be
obtained also in the case of applying the same voltage to the LED
of each color.
[0068] The present invention is not limited to the above-mentioned
embodiment, and is capable of being carried into practice with
various modifications thereof.
[0069] An aspect of an adjustment method of a display device of the
present invention includes an LED emission step of performing PWM
control independently on an LED of each of colors, red, green and
blue, in a unit emission period to cause the LED to emit light, a
measuring step of measuring chromaticity of the light, a
calculating step of calculating a difference between a measured
value obtained in the measuring step and a target white balance
value, a correcting step of correcting a duty ratio of a PWM signal
on the LED of each of colors in the LED emission step corresponding
to the difference obtained in the calculating step, and a duty
ratio storing step of storing a duty ratio for the LED of each of
colors in a storage when the difference calculated in the
calculating step falls within a predetermined allowable range.
[0070] According to this method, emission in a unit emission period
of the LED of each of colors is controlled using the PWM signal,
while storing in the storage the duty ratio of the PWM signal for
the LED of each of colors such that the white balance falls within
an allowable range. Therefore, even when there are fluctuations
between LEDs of the colors due to individual differences, it is
possible to make a display adjustment with ease such that the white
balance falls within an allowable range.
[0071] In another aspect of the adjustment method of a display
device of the present invention, the adjustment of the display
device is made in such a state that an LCD panel is attached to a
front face of the LED and that the LCD panel is driven.
[0072] According to this method, even when there are fluctuations
between LCD panels due to individual product differences, it is
possible to absorb the fluctuations and bring the white balance
into an allowable range.
[0073] In still another aspect of the adjustment method of a
display device of the present invention, in the correcting step,
the duty ratio of the PWM signal for the LED of each of colors is
corrected in consideration of a distribution range of the
chromaticity of the LED of each of colors.
[0074] According to this method, it is possible to find the duty
ratio such that the white balance falls within the allowable range
promptly in a small number of corrections. For example, the amount
of the difference is allocated in proportion to the amount of
correction of the duty ratio for the LED of each of colors in
consideration of the distribution range of the chromaticity of the
LED of each of colors.
[0075] In still another aspect of the adjustment method of a
display device of the present invention, the duty ratio is
corrected independently on LEDs of the same color corresponding to
the difference obtained in the calculating step, and independent
duty ratios for the LEDs of the same color are stored in the duty
ratio storing step.
[0076] According to this method, it is possible to adjust the LEDs
of the same color using independent PWM signals, and it is thereby
possible to execute finer white balance adjustment processing than
in the case of performing PWM control on the LEDs of the same color
collectively using the same PWM signal.
[0077] An aspect of a display device of the present invention
adopts a configuration having a duty ratio storage which is
comprised of writable memory and stores therein a duty ratio to
perform PWM control independently on an LED of each of colors, red,
green and blue, in a unit emission period, independently for each
LED, a PWM controller which forms a PWM signal based on the duty
ratio stored in the duty ratio storage independently for each LED
to perform PWM control independently on the LED of each of colors
in the unit emission period, and a signal line connected to the
duty ratio storage to input the duty ratio to the duty ratio
storage.
[0078] Another aspect of the display device of the present
invention adopts a configuration where the duty ratio storage
stores the duty ratio provided with a white balance adjustment via
the signal line.
[0079] According to these configurations, emission in a unit
emission period of the LED of each of colors is controlled using
the PWM signal, and it is thereby possible to adjust the white
balance finely with ease. Further, the duty ratio of the PWM signal
for the LED of each of colors is stored in the writable memory, and
it is thus possible to write the duty ratio adapted to the display
device at any time.
[0080] Still another aspect of the display device of the present
invention adopts a configuration where the duty ratio storage
stores independent duty ratios for LEDs of the same color, and the
PWM controller forms independent PWM signals for the LEDs of the
same color to perform PWM control independently on the LEDs of the
same color in a unit emission control.
[0081] According to this configuration, the LEDs of the same color
are also controlled in emission using the independent PWM signals,
and it is thus possible to perform finer white balance display.
[0082] As described above, according to the present invention,
emission in a unit emission period of the LED of each of colors is
controlled using the PWM signal, while storing in the storage the
duty ratio of the PWM signal for the LED of each of colors such
that the white balance falls within an allowable range. Therefore,
it is possible to implement an adjustment method of a display
device and the display device enabling the white balance adjustment
to be made finely with ease even when there are fluctuations in
emission characteristics of LED and LCD panel.
[0083] Further, rough luminance adjustment is first made by storing
a minimum voltage value for each color when a luminance higher than
a target is obtained in a state where the duty ratio is maximum,
and fine luminance adjustment is then made by varying the duty
ratio of the PWM signal while applying the stored applied voltage
of fixed value, whereby current consumption can be reduced, in
addition to the fact that the white balance is adjusted with
excellence.
[0084] This application is based on the Japanese Patent Application
No. 2003-98488 filed on Apr. 1, 2003, entire content of which is
expressly incorporated by reference herein.
INDUSTRIAL APPLICABILITY
[0085] The present invention is suitable for being applied to, for
example, a liquid crystal display device.
FIG. 1 FIG. 3
[0086] 10 LED DRIVING DEVICE [0087] 11 R APPLIED VOLTAGE STORAGE
REGISTER [0088] 12 G APPLIED VOLTAGE STORAGE REGISTER [0089] 13 B
APPLIED VOLTAGE STORAGE REGISTER [0090] 15 REGISTER SELECTING
CIRCUIT [0091] 17 DA CONVERTING CIRCUIT [0092] 18 VOLTAGE VARYING
CIRCUIT [0093] 19 POWER SUPPLY VOLTAGE GENERATING CIRCUIT [0094] 21
R DUTY RATIO STORAGE REGISTER [0095] 22 G DUTY RATIO STORAGE
REGISTER [0096] 23 B DUTY RATIO STORAGE REGISTER [0097] 24 25 26
PWM WAVEFORM FORMING CIRCUIT FIG. 2 [0098] MINIMUM VALUE STANDARD
VALUE MAXIMUM VALUE [0099] RED LED GREEN LED BLUE LED [0100] UNIT
FIG. 3 [0101] 30 DRIVING VOLTAGE SETTING DEVICE [0102] 31
LUMINANCE/CHROMATICITY METER [0103] 32 MICROCOMPUTER [0104] 33
APPLIED VOLTAGE SETTING SECTION [0105] 34 DUTY RATIO SETTING
SECTION [0106] 40 LCD PANEL FIG. 4 [0107] ST10 START [0108] ST11
SET ON DUTY RATIOS R: MAXIMUM [0109] ST12 SET THE TARGET LUMINANCE
[0110] ST13 APPLY VOLTAGE Vmin [0111] ST14 MEASURED
LUMINANCE>TARGET LUMINANCE? [0112] ST16 STORE THE APPLIED
VOLTAGE VALUE [0113] ST17 MEASURED LUMINANCE=TARGET LUMINANCE?
[0114] ST19 STORE THE ON DUTY RATIOS [0115] ST20 END FIG. 5 [0116]
ST30 START [0117] ST31 LIGHT AN LED OF EACH COLOR WITH STORED
APPLIED VOLTAGE AND DUTY RATIO DRIVE THE LIQUID CRYSTAL [0118] ST32
MEASURE THE CHROMATICITY [0119] ST33 Y COORDINATE IS IN AN
ALLOWABLE RANGE ? [0120] ST34 X COORDINATE IS IN AN ALLOWABLE RANGE
? [0121] ST35 VARY THE DUTY RATIO [0122] ST36 WRITE THE DUTY RATIO
[0123] ST37 END FIG. 6 [0124] ELEMENT CHROMATICITY RANGE [0125]
Green LED DISTRIBUTION RANGE [0126] Blue LED DISTRIBUTION RANGE
[0127] Red LED DISTRIBUTION RANGE [0128] RGB PWM VALUE FINE
ADJUSTMENT DIRECTION [0129] WHITE ALLOWABLE RANGE
* * * * *